Assessment of Methods for Accurate Reproductive Tract Scoring By Vulva Width As a Tool for Gilt Selection

Improving sow lifetime productivity (SLP) is essential for maximizing sow farm profitability, however, SLP is a complex trait heavily influenced by a variety of postpubertal and prepubertal environmental factors. One of the best predictors of SLP for replacement gilts is age at puberty. Our group has shown a higher percentage of gilts who possess an average or above vulva size at 95-115 days of age achieve puberty by 180 days of age compared to counterparts with a below average vulva size. The objective of this study was to determine the accuracy of different vulva scoring methods on a commercial farm. To accomplish this, prepubertal replacement gilts (n=1198) in a commercial system were selected at 15 weeks of age. Body weight for each gilt was recorded and four different vulva scoring methods were used to classify gilts based on vulva width (VW). Methods included a digital caliper measurement of VW, evaluation and scoring by trained farm personnel (small, medium, and large), and two methods using scoring tools (A and B) specifically calibrated based on the distribution of gilt VW in previous studies. Tool A was designed to assign gilts one of three VW scores (small, medium, and large). Tool B was designed to discriminate gilts into five groups corresponding with a numerical score (1-5, with 1 being the smallest and 5 being largest). At 15 weeks of age, a low proportion of variability in vulva size (27.58 + 0.12 mm) could be explained by body weight (61.6 + 0.02 kg) (R² = 0.06). Importantly, correlation between the measurement with digital calipers was strong for the farm personnel score (R² = 0.50), tool A score (R² = 0.64) and tool B scores (R² = 0.82) demonstrating each method’s effectiveness in accurately discerning gilts into groups based on vulva size. The trained farm personnel score assigned 21.8, 71.2 and 7.0% of the gilts as small, medium, and large, respectively. Scoring tool A assigned 23.5, 70.3 and 6.2% of the gilts to the small, medium and large categories, while scoring tool B assigned 22.7, 25.5, 34.3, 12.3 and 5.2% of the gilts to numerical categories 1-5, respectively. Assessment of gilt reproductive performance in the sow herd is underway and will enable the retrospective analysis of the utility of each scoring method as predictor of SLP. This project was supported in part by the Iowa Pork Producers Association and Tri-Oak Foods.